Influence of alpine plants growing on steep slopes on sediment trapping and transport by runoff

Understanding the interactions between soil and the organisms that are conducive to decreasing sediment runoff is a great concern on high-elevation ski trails. Intense rainfalls on steep slopes combined with soil formed on gypsum result in recurrent erosion. This study was conducted in the northern French Alps to determine the abilities of species: (1) to make mounds and (2) to trap sediment and thereby to control erosion at the slope scale. We also investigated relevant above-ground plant characteristics related to those abilities. Sediment runoff or deposition was investigated at small and large spatial scales. We assessed whether hoof prints in soil reflect sediment runoff at the slope scale by trapping sediment. Populations of plants growing on two slope angles (25° and 35°) and three vegetation cover densities (15%, 35%, 60%) were surveyed. An experiment was also conducted to measure the sediment deposit upslope of target species and over three months during the autumn. Small mounds were found upslope of the plant and sediment deposit measurements showed that they resulted from a sedimentation process. Nevertheless the species differed in their capacity to make mounds. Sesleria caerulea and Festuca alpina had the highest amount of sediment deposition over the experimental period. Among the plant characteristics, plant length was positively correlated with mound area, while the roundness index of the canopy was negatively correlated with mound height. Mound formation was also positively related to the number of tillers or shoots. Sediment accumulation in cow hoof prints was linked to runoff that occurred at the slope scale. Low deposition in hoof prints means low sediment runoff or a large deposition on mounds, due to the increase in vegetation cover. All the findings stressed that understanding the processes in action at larger scales requires studying processes at smaller scales.     

多场次降雨对崩岗崩积体细沟侵蚀的影响

崩积体是崩岗的重要组成部分,因土质疏松,极易被侵蚀。细沟侵蚀特征是探讨崩积体侵蚀机制的重要内容。采用人工模拟降雨试验,研究多场次降雨条件（1.00、1.67、2.33 mm/min分别降3次雨）对崩积体30°坡面（5m×1 m）细沟侵蚀产沙过程及发育形态特征的影响。结果表明：1）1.00 mm/min降雨强度条件下,3次降雨的后期产沙过程趋于一致,而1.67和2.33 mm/min降雨强度条件下,前2次降雨后期产沙过程趋于一致,但第3次降雨后期产沙率急剧增大;2）各降雨强度条件下,沟头溯源作用、细沟平均宽度及深度随着降雨场次的增加而增加;3）不同降雨强度条件下的细沟特征存在差异,1.00和1.67 mm/min降雨强度时,随着降雨场次的增加,坡面的细沟数及细沟密度增加,宽深比减小,但在2.33 mm/min降雨强度条件下的结果恰好相反;4）各降雨强度条件下细沟侵蚀量及其增加幅度均增大,细沟侵蚀愈剧烈。     

基于贡献率模型的崩塌易发性评价——以广州市白云区为例

[目的] 根据地质灾害野外普查空间数据库,分析花岗岩风化残积土发育地区崩塌形成机理和破坏模式,探究不同环境孕灾因子对崩塌发育的贡献率,评估崩塌灾害空间易发性与分布规律,为中国东南沿海地质灾害多发区的灾害防治工作提供科学支持。[方法] 在分析广州市白云区花岗岩风化残积土崩塌发育特征的基础上,选取高程、坡度、坡向、地形起伏度、距地表水体距离、降雨量、地层岩性、土地利用类型共8个与崩塌灾害发育密切关联的致灾因子构建崩塌灾害易发性评价指标体系,叠加研究区内404个历史崩塌数据,依据贡献率模型计算统计各指标因子崩塌灾害敏感性和空间分布特征。采用各二级指标因子贡献率的修正样本差确定因子权重。[结果] ①研究区内坡度、高程和地形起伏度对崩塌易发性贡献程度较高,坡向、地层岩性、降雨量在崩塌灾害易发性评价中贡献程度较低。②极高易发区主要集中在丘陵西麓,崩塌易发性由山地线范围外层边缘向中心逐级降低。③崩塌极高易发区和高易发区崩塌比率占总崩塌比率超过85%,模型易发性评价成功率和预测率分别达到91.3%和92.6%。[结论] 斜坡地形地貌因子对崩塌发育影响较显著,基于贡献率的崩塌灾害易发性评价模型能够客观量化指标因子权重,模型预测评价结果精度较高,易发性区划符合实际崩塌发育空间分布特征。     

正循环钻孔桩钻进中预防坍孔的分析方法

为了避免钻孔桩在钻进中出现坍孔，应在钻孔前水头压力，护壁泥浆的性能，钻进土层的物理性能指标进行验算和分析。文中提出了钻进中预防出现坍孔的分析方法，并结合工程实例，进行了说明。     

Theoretically Investigation of Dynamic Characteristics of Spherical Bubble Collapse in Pulsed Abrasive Water Jet

This paper theoretically investigates the characteristics of cavitating bubbles in the pulsed abrasive water jet(PAWJ) and establishes the dynamic equations of cavitating bubbles. The effects of abrasive diameter and density on the spherical bubble collapse are also analyzed. It is found that the change of abrasive diameter rarely affects the bubble collapse when the abrasive diameter and density are small whereas the smaller abrasive greatly blocks the bubble collapse when the abrasive diameter and density are comparably big. It is also shown that when the abrasive density is increased, the fluid viscosity rises, and the kinetic energy of the abrasives near the collapsed bubble is enhanced and meanwhile the intensity of cavitating erosion is weakened.     

两种工程堆积体坡面细沟形态与产沙关系对比研究

为探究不同土壤类型工程堆积体坡面细沟形态与水动力学参数及侵蚀产沙间的关系,选取沟宽、沟深、宽深比等作为细沟形态参数,在放水流量8、12、16、20 L·min^-1和坡度32°条件下,对红土和塿土工程堆积体进行冲刷试验。结果表明:(1)两种堆积体坡面细沟沟宽、沟深在前24 min均发育迅速;随放水流量增大,沟宽和沟深均呈增大趋势,红土沟宽均值(较8 L·min^–1)分别增加0.8%、19.3%、27.2%,沟深均值分别增加24.5%,126.2%,95.1%,而塿土则为3.7%、62.4%、108.2%和18.2%、87.9%、95.5%;红土沟宽、沟深与冲刷历时均呈极显著线性函数关系(R2>0.858,P<0.01),而塿土则为极显著对数函数关系(R2>0.689,P<0.01);(2)两种堆积体坡面细沟宽深比呈先波动(0~24 min)后(25~45 min)平稳的变化趋势;放水流量增至16 L·min^-1,两种堆积体宽深比均值减幅最大(较8 L·min^-1),红土最大减少了1.15,塿土最大减少了0.20;(3)两种堆积体坡面细沟水流剪切力、水流功率与沟宽、沟深均呈现幂函数关系(R2>0.602,P<0.01);径流剪切力更适合描述红土沟深的发育状况,而径流功率更能体现塿土沟宽的发育过程;(4)两种堆积体坡面累计产沙量与沟宽和沟深均呈极显著线性函数关系(R2>0.897,P<0.01);沟宽、沟深对红土坡面累计产沙量的贡献率分别为84.9%、15.1%,对塿土则为22.5%和77.5%;该研究可为不同土壤类型工程堆积体坡面水土保持措施合理配置提供理论依据。     

冰藏鲢的鲜度变化对其鱼糜凝胶作用的影响

通过比较不同冰藏时间的鲢所制鱼糜在各种加热温度下的凝胶化和凝胶劣化的特性,考察了鲢的鲜度变化与鱼糜凝胶作用能力的关系。实验结果表明：冰藏０￣９天鲢鱼糜,在３０℃低温一段加热时凝胶的形成与链鲜度关系不大;８５℃一段加热时,凝胶化能力随鲜度下降而降低;３０￣８５℃二段加热与３０℃一段加热相比,两者凝胶破断强度之间的差值随鲢鲜度的下降而减小;６０℃加热条件下,凝胶劣化程度随原料鲜度下降而明显加剧。据此可见：鲜度对鲢鱼糜凝胶作用能力的影响主要表现在凝胶劣化方面。８５℃高温一段加热和３０￣８５℃二段加热的凝胶强度之所以受鲜度下降而影响,都是由于加热时经过了易劣化的６０℃温度区所致。从总体上看,鲢肉蛋白质在冰藏条件下较为稳定,保持较强的凝胶化能力。     

Research on reliability evaluation model for frequency collapse of power grid

In order to comprehensively consider the possibility and the severity of frequency instability risk, this paper proposes the risk evaluation model and algorithm for frequency collapse of power grid. The uncertainties in generating dispatch, network topology and component outage are considered. The calculation method for system frequency variation is depicted while considering the active power deficiency arising from random failure of generating units, and then various probabilistic risk indices for frequency collapse are defined. The presented method can provide important reference information for evaluating the frequency collapse risk of power grid. The non-sequential Monte Carlo simulation-based results of IEEE-RTS79 show the correctness of the method.     

Structural Influencing Coefficient of Moment-Resisting Steel Frames Based on Equal Collapse Rule

In order to realize the performance target of “no collapse under rare earthquake” based on the seismic design according to structural influencing coefficient, three moment-resisting steel frames have been designed with similar probability of collapse in accordance with Chinese Seismic Code. The structural influencing coefficient of steel frames were determined through the incremental dynamic analysis method, and within equal collapse design rule. This paper proposed a method to define structural influencing coefficient can provide reference for determining the design seismic force of steel frame reasonably.     

A novel treatment for dynamic laryngeal collapse associated with poll flexion: the modified checkrein

Reasons for performing the study: Dynamic laryngeal collapse (DLC) associated with poll flexion is a performance limiting dynamic upper airway disorder commonly diagnosed in Coldblooded trotters. An inspiratory obstruction occurs when affected horses are driven with tension on the reins, inducing poll flexion. To date, surgical treatment and conservative management have failed to improve racing performance in affected horses. Objectives: To test the efficacy of an external device, the modified checkrein, in limiting poll flexion, diminishing laryngeal collapse and improving airway mechanics when horses are driven on a treadmill with tension on the reins and test the hypothesis that the modified checkrein will limit poll flexion thereby improving endoscopic appearance of the larynx and reduce airway obstruction in harness racehorses affected with DLC. Methods: Fourteen Norwegian Coldblooded trotter (NCT) racehorses previously diagnosed with DLC associated with poll flexion exercised on a high‐speed treadmill at speeds that resulted in heart rate >200 beats/min. Upper airway videoendoscopy recordings, tracheal pressures and video recordings of the head and neck position were collected while horses exercised with the conventional checkrein on Day 1 and the modified checkrein on Day 2. Results: The modified checkrein successfully limited poll flexion as measured by no change in head position parameters between phases of no rein tension and phases of rein tension. Endoscopic scores were significantly improved (arytenoids cartilage collapse P<0.0001; vocal fold collapse P<0.0001) and tracheal peak inspiratory pressures were significantly less negative (P = 0.0162) when horses were fitted with the modified checkrein compared to the conventional checkrein. Conclusions and potential relevance: The modified checkrein successfully limited poll flexion and also prevented upper airway obstruction in NCT horses affected with DLC associated with poll flexion. The modified checkrein seems promising in offering a method of conservative management in harness racehorses affected with this disorder.